A semiconductor device such as memory device, logic device, microprocessor, etc. is formed with conductive external connections to facilitate electrical coupling with test equipment, and eventually connection with a substrate such as a printed circuit board (PCB). Through-hole packages having leads which project through a printed circuit board, such as single in-line packages (SIPs) and dual in-line packages (DIPs), progressed to surface mount leads such as “j” style leads, which in turn progressed to bump-style connections such as flip chip and ball grid array (BGA) devices.
Current methods of connecting a semiconductor device having bump-style leads with landing pads of a receiving substrate such as a PCB include wet solder processes. In a first wet solder process, solder flux is applied to the conductive bumps of the semiconductor device to reduce surface tension (i.e. improve “wettability”) and to remove oxides. Subsequently, the bumps of the device are placed in contact with the landing pads of the receiving substrate using the solder flux to temporarily adhere the structures together, then the assembly is placed into a molten solder wave such that solder adheres to the bumps and the landing areas to electrically and mechanically interconnect the two structures. An underfill may then be used to reduce sheer stresses between the electrical contacts.
In a second wet solder process, electrolytic deposition is used to plate the copper bumps with solder. The plated bumps are placed into physical contact with the landing pads, and the solder is reflowed to electrically and mechanically join the semiconductor device and receiving structure.
In a third wet solder process, an electroless deposition process is performed by immersing the bumps in an aqueous solution containing plating chemicals to plate the bumps with solder. The plated bumps are then joined to the landing pads by placing the two structures into physical contact. The solder is then reflowed to electrically and mechanically join the semiconductor device and receiving structure. Underfill may also be used with electrolytic and electroless plated devices.